In conventional Time Division Multiple Access (TDMA) systems, compression and expansion buffering is accomplished by using two separate memories in a ping-pong arrangement. With such an arrangement, one memory is continuously read while the other is continuously written and the two memories are alternately switched between read and write states on a TDMA frame boundary, thus avoiding the problems of asynchronously reading and writing the same memory. A disadvantage inherent in the use of ping-pong memories, however, is that it requires two buffer memories, each of which is at least large enough to accomodate a TDMA frame. This can proove particularly costly in long-frame TDMA systems in which large buffers are required.
A second disadvantage of the ping-pong memory configuration is that, due to the rigid timing requirements of alternately switching from one memory to the other, elastic buffers, which compensate for satellite motion and oscillator drift, cannot be incorporated as part of the TDMA compression/expansion buffers. It is thus necessary to construct the elastic buffer or alternate pulse stuffing units separately when using the ping-pong method.